Method for the production of liquefied natural gas

ABSTRACT

A method for the production of liquefied natural gas (LNG) without the use of externally provided electricity is provided The method may include the steps of: providing a transportable apparatus, wherein the transportable apparatus comprises a housing, a heat exchanger, a phase separator, a first refrigeration supply, and a second refrigeration supply, wherein the first refrigeration supply and the second refrigeration supply are configured to provide refrigeration within the heat exchanger; introducing a natural gas stream into the transportable apparatus at a first pressure under conditions effective for producing an LNG stream; withdrawing the LNG stream from the transportable apparatus; and withdrawing a warm natural gas stream from the transportable apparatus, wherein the warm natural gas stream is at a second pressure, wherein the second pressure is lower than the first pressure.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/201,947, filed on Aug. 6, 2015, U.S. Provisional PatentApplication No. 62/305,381, filed on Mar. 8, 2016, and U.S. ProvisionalApplication Ser. No. 62/370,953 filed on Aug. 4, 2016, all of which arehereby incorporated by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to a method and apparatus forproducing liquefied natural gas (LNG) in a packaged unit without anyrotating machinery.

BACKGROUND OF THE INVENTION

There are numerous reasons for the liquefaction of gases, includingnaturally occurring gases such as methane. Perhaps the chief reason isthat liquefaction greatly reduces the volume of a gas, making itfeasible to store and transport the liquefied gas in containers ofimproved economy and design. Liquid gases can be stored in suitablydesigned cryogenic containers and dispensed into vehicle tanks usingtechniques that have been in use for many years in the industrialcryogenic gas industries.

Many industrial gases such as propane, butane and carbon dioxide can beliquefied by placing them under very high pressure. However, producingliquid from methane may not be achieved with high pressure alone. Tothis extent, methane, a cryogenic gas, is different from otherindustrial gases. To liquefy methane it is typically necessary to reducethe temperature of the gaseous phase to below about −160° C., dependingupon the pressure at which the process is operated.

Numerous systems exist in the prior art for the production of liquefiednatural gas (“LNG”). Conventional processes known in the art requiresubstantial refrigeration to reduce the gas to liquid. Among the mostcommon of these refrigeration processes are: (1) the cascade process;(2) the single mixed refrigerant process; and (3) the propane pre-cooledmixed refrigerant process.

The cascade process produces liquefied gases by employing severalclosed-loop cooling circuits, each utilizing a single pure refrigerantand collectively configured in order of progressively lowertemperatures. The first cooling circuit commonly utilizes propane orpropylene as the refrigerant; the second circuit may utilize ethane orethylene, while the third circuit generally utilizes methane as therefrigerant.

The single mixed refrigerant process produces LNG by employing a singleclosed-loop cooling circuit utilizing a multi-component refrigerantconsisting of components such as nitrogen, methane, ethane, propane,butanes and pentanes. The mixed refrigerant undergoes the steps ofcondensation, expansion and recompression to reduce the temperature ofnatural gas by employing a unitary collection of heat exchangers knownas a “cold box.”

The propane pre-cooled mixed refrigerant process produces LNG byemploying an initial series of propane-cooled heat exchangers inaddition to a single closed-loop cooling circuit, which utilizes amulti-component refrigerant consisting of components such as nitrogen,methane, ethane and propane. Natural gas initially passes through one ormore propane-cooled heat exchangers, proceeds to a main exchanger cooledby the multi-component refrigerant, and is thereafter expanded toproduce LNG.

Most liquefaction plants utilize one of these gas liquefactionprocesses. Unfortunately, the cost and maintenance of such plants isexpensive because of the cost of constructing, operating and maintainingone or more external, single or mixed refrigerant, closed-loop coolingcircuits. Such circuits typically require the use and storage ofmultiple highly explosive refrigerants that can present safety concerns.Refrigerants such as propane, ethylene and propylene are explosive,while propane and propylene, in particular, are heavier than air,further complicating dispersion of these gases in the event of a leak orother equipment failure. It would therefore be beneficial to eliminatethe external refrigeration circuit(s) in a liquefaction plant.

One of the distinguishing features of a conventional liquefaction plantin the prior art is the large capital investment required. The equipmentused to liquefy cryogenic gases in high volumes is large, complex andvery expensive. The plant is typically made up of several basic systems,including a gas treatment system (to remove impurities from the initialfeed stream), and liquefaction, refrigeration, power, storage andloading facilities. Materials required in conventional liquefactionplants also contribute greatly to the plants' cost. Containers, longruns of piping, and multiple-level tiers of other equipment areprincipally constructed from aluminum, stainless steel or high nickelcontent steel to provide the necessary strength and fracture toughnessat low temperatures. It would therefore be beneficial to decrease theinitial amount of capital investment needed to form a liquefactionplant.

Another distinguishing feature of a conventional liquefaction plant inthe prior art is that as a result of its complexity and size, the plant,by necessity, is typically a fixed installation that cannot be easilyrelocated. Even if a conventional plant can be physically relocated,such a move is very costly and requires the plant to be out of servicefor many months while plant systems, components and structures aredisassembled, moved and then reassembled on a newly prepared site. Itwould therefore be beneficial to provide a liquefaction plant that issmall and simple in design so that it can be easily relocated withoutsignificant operational down time.

There exists a multitude of current prior art methods for theliquefaction of natural gas. For example, U.S. Pat. No. 5,755,114 toFoglietta discloses a hybrid liquefaction cycle for the production ofLNG. The Foglietta process passes a pressurized natural gas feed streaminto heat exchange contact with a closed-loop propane or propylenerefrigeration cycle prior to directing the natural gas feed streamthrough a turboexpander cycle to provide auxiliary refrigeration. TheFoglietta process requires at least one external closed-looprefrigeration cycle comprising propane or propylene, both of which areexplosive.

The system of U.S. Pat. No. 6,085,545 to Johnston first compresses thenatural gas feed (typically methane) which then passes through anafter-cooler to remove the heat of compression. At this point thenatural gas flow is split into two flow portions, the first of which iscooled in at least one heat exchanger and then throttled into acollector, and the second of which enters a turboexpander wherein thetemperature and pressure are lowered and the work of expansion isextracted. The second flow portion is then used in at least one heatexchanger as the heat exchange cooling medium.

U.S. Pat. No. 3,616,652 to Engel discloses a process for producing LNGin a single stage by compressing a natural gas feed stream, cooling thecompressed natural gas feed stream to form a liquefied stream,dramatically expanding the liquefied stream to an intermediate-pressureliquid, and then flashing and separating the intermediate-pressureliquid in a single separation step to produce LNG and a low-pressureflash gas. The low-pressure flash gas is recirculated, substantiallycompressed and reintroduced into the intermediate pressure liquid. Whilethe Engel process produces LNG without the use of external refrigerants,the process yields a small volume of LNG compared to the amount of workrequired for its production, thus limiting the economic viability of theprocess.

While these prior art inventions may be sufficient for the particularproblems that they solve, it would be beneficial in the industry toprovide an improved process for the cryogenic refrigeration andliquefaction of gases. It would also be beneficial to eliminate theexternal refrigeration circuit(s) in a liquefaction plant. It would belikewise be advantageous to decrease the initial amount of capitalinvestment needed to form a liquefaction plant. It would also beadvantageous to provide a liquefaction plant that is small and simple indesign so that it can be easily relocated without significantoperational down time.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus thatsatisfies at least one of these needs. In certain embodiments, theinvention can provide a lower cost, more efficient and flexible methodto produce LNG using a transportable apparatus. For example, in certainembodiments, the invention utilizes a natural gas letdown to produce LNGin a packaged unit, without the need for electrically poweredcompressors or the use of rotating machinery.

In one embodiment, a transportable apparatus for the production ofliquefied natural gas (“LNG”) is provided. In this embodiment, theapparatus can include a housing, a natural gas feed inlet, a heatexchanger, a phase separator, a liquid outlet disposed on the cold endof the heat exchanger, an LNG product outlet disposed on the cold end ofthe heat exchanger, a first refrigeration supply, a second refrigerationsupply, and wherein the heat exchanger, the phase separator, the firstexpansion valve, the first refrigeration supply, and the secondrefrigeration supply are all disposed within the housing.

In one embodiment, the natural gas feed inlet configured to accept astream of pressurized natural gas originating from outside the housing.In another embodiment, the heat exchanger is in fluid communication withthe natural gas feed inlet, such that the heat exchanger is configuredto receive the stream of pressurized natural gas from the natural gasfeed inlet, wherein the heat exchanger has a warm end, a cold end, andan intermediate section. In another embodiment, the phase separator hasa fluid inlet, a gaseous outlet, and a liquid outlet, wherein the fluidinlet is in fluid communication with a first intermediate fluid outletlocated in the intermediate section of the heat exchanger, such that thephase separator is configured to receive a partially cooled fluid fromthe heat exchanger, wherein the liquid outlet of the phase separator isin fluid communication with a first intermediate fluid inlet of theintermediate section of the heat exchanger, wherein the gaseous outletof the phase separator is in fluid communication with a secondintermediate fluid inlet of the intermediate section of the heatexchanger, such that the second intermediate fluid inlet of theintermediate section of the heat exchanger is configured to receive atleast a first portion of gas coming from the phase separator. In anotherembodiment, the liquid outlet is disposed on the cold end of the heatexchanger and in fluid communication with the second intermediate fluidinlet of the intermediate section of the heat exchanger. In anotherembodiment, the LNG product outlet is in fluid communication with theliquid outlet disposed on the cold end of the heat exchanger. In anotherembodiment, the first refrigeration supply comprises a first expansionvalve, a first LNG inlet disposed on the cold end of the heat exchanger,and a first natural gas outlet disposed on the warm end of the heatexchanger, wherein the first refrigeration supply is in fluidcommunication with the liquid outlet disposed on the cold end of theheat exchanger, wherein the heat exchanger is configured to indirectlyexchange heat between a first LNG stream and a natural gas stream whenthe first LNG stream flows from the first LNG inlet to first natural gasoutlet.

In another embodiment, the second refrigeration supply is configured toprovide refrigeration within the heat exchanger. In one embodiment, theflow of first and second LNG stream combined can account for less than10% of the flow of the natural gas flowing through the natural gas feedinlet. In another embodiment, the expanded second portion of top gas canconstitute a third refrigeration supply. In another embodiment, theexpanded heavy hydrocarbons can constitute a fourth refrigerationsupply.

In optional embodiments of the transportable apparatus:

-   -   the second refrigeration supply comprises a liquid nitrogen        inlet disposed on the cold end of the heat exchanger and a        nitrogen outlet disposed on the warm end of the heat exchanger,        and wherein the heat exchanger is configured to indirectly        exchange heat between a liquid nitrogen fluid and the natural        gas stream when the liquid nitrogen flows from the liquid        nitrogen inlet to the nitrogen outlet;    -   the second refrigeration supply further comprises a liquid        nitrogen storage tank in fluid communication with the liquid        nitrogen inlet, such that the liquid storage tank is configured        to deliver liquid nitrogen to the heat exchanger via the liquid        nitrogen inlet;    -   the second refrigeration supply comprises a second expansion        valve, a second LNG inlet disposed on the cold end of the heat        exchanger, and a second natural gas outlet disposed on the warm        end of the heat exchanger, and wherein the heat exchanger is        configured to indirectly exchange heat between a second LNG        stream and the natural gas stream when the second LNG stream        flows from the second LNG inlet to second natural gas outlet;    -   the first expansion valve is configured to expand the first LNG        stream to a first pressure, wherein the second expansion valve        is configured to expand the second LNG stream to a second        pressure, wherein the first pressure is higher than the second        pressure;    -   the first pressure is between 4 and 10 bara, wherein the second        pressure is between 1 to 2 bara;    -   the transportable apparatus may also include a third        intermediate fluid inlet of the intermediate section of the heat        exchanger that is configured to receive a second portion of gas        coming from the phase separator;    -   the transportable apparatus may also include a third expansion        valve in fluid communication with, and disposed inline between,        the gaseous outlet of the phase separator and a second        intermediate fluid inlet of the intermediate section of the heat        exchanger;    -   the transportable apparatus may also include a lower pressure        natural gas outlet in fluid communication with the first natural        gas outlet of the heat exchanger, wherein the lower pressure        natural gas outlet is configured to send a stream warm natural        gas received from the first natural gas outlet to outside of the        housing;    -   the transportable apparatus may also include a liquid expansion        valve in fluid communication with, and disposed inline between,        the liquid outlet of the phase separator and the first        intermediate fluid inlet of the intermediate section of the heat        exchanger;    -   the heat exchanger is split into a first portion and a second        portion, wherein the warm end of the heat exchanger is disposed        in the first portion, wherein the cold end of the heat exchanger        is disposed in the second portion, wherein the intermediate        section is disposed in both the first portion and the second        portion;    -   the transportable apparatus may also include an absence of        compression means;    -   the transportable apparatus may also include an absence of a        rotating compressor;    -   the transportable apparatus may also include an absence of        rotating machinery;    -   the transportable apparatus may also include an absence of        electrically powered compression or expansion devices;    -   the transportable apparatus is configured to liquefy natural gas        without the use of externally provided electricity; and/or    -   the housing is configured to fit within a shipping container        such that the transportable apparatus is configured to be        transported via a truck and/or a barge.

In another aspect of the invention, a method for the production ofliquefied natural gas (“LNG”) using a transportable apparatus isprovided. In this embodiment, the method can include the steps of:providing a transportable apparatus, wherein the transportable apparatuscomprises a housing, a heat exchanger, a phase separator, a firstrefrigeration supply, and a second refrigeration supply, wherein thefirst refrigeration supply and the second refrigeration supply areconfigured to provide refrigeration within the heat exchanger;introducing a natural gas stream into the transportable apparatus at afirst pressure under conditions effective for producing an LNG stream;withdrawing the LNG stream from the transportable apparatus; andwithdrawing a warm natural gas stream from the transportable apparatus,wherein the warm natural gas stream is at a second pressure, wherein thesecond pressure is lower than the first pressure.

In optional embodiments of the method for the production of LNG:

-   -   the first refrigeration supply comprises a first expansion        valve, a first LNG inlet disposed on a cold end of the heat        exchanger, and a first natural gas outlet disposed on a warm end        of the heat exchanger, wherein the first refrigeration supply is        in fluid communication with a liquid outlet disposed on the cold        end of the heat exchanger, wherein the heat exchanger is        configured to indirectly exchange heat between a first LNG        stream and the natural gas stream when the first LNG stream        flows from the first LNG inlet to first natural gas outlet;    -   the second refrigeration supply comprises a liquid nitrogen        inlet disposed on the cold end of the heat exchanger and a        nitrogen outlet disposed on the warm end of the heat exchanger,        and wherein the heat exchanger is configured to indirectly        exchange heat between a liquid nitrogen fluid and the natural        gas stream when the liquid nitrogen flows from the liquid        nitrogen inlet to the nitrogen outlet;    -   the second refrigeration supply further comprises a liquid        nitrogen storage tank in fluid communication with the liquid        nitrogen inlet, such that the liquid storage tank is configured        to deliver liquid nitrogen to the heat exchanger via the liquid        nitrogen inlet;    -   the second refrigeration supply comprises a second expansion        valve, a second LNG inlet disposed on the cold end of the heat        exchanger, and a second natural gas outlet disposed on the warm        end of the heat exchanger, and wherein the heat exchanger is        configured to indirectly exchange heat between a second LNG        stream and the natural gas stream when the second LNG stream        flows from the second LNG inlet to second natural gas outlet;    -   the first expansion valve is configured to expand the first LNG        stream to a first LNG pressure, wherein the second expansion        valve is configured to expand the second LNG stream to a second        LNG pressure, wherein the first LNG pressure is higher than the        second LNG pressure;    -   the first LNG pressure is between 4 and 10 bara, wherein the        second LNG pressure is between 1 to 2 bara;    -   the transportable apparatus further comprises a natural gas feed        inlet configured to accept a stream of pressurized natural gas        originating from outside the housing, wherein the heat exchanger        is in fluid communication with the natural gas feed inlet, such        that the heat exchanger is configured to receive the stream of        pressurized natural gas from the natural gas feed inlet, wherein        the heat exchanger has a warm end, a cold end, and an        intermediate section, wherein phase separator has a fluid inlet,        a gaseous outlet, and a liquid outlet, wherein the fluid inlet        is in fluid communication with a first intermediate fluid outlet        located in the intermediate section of the heat exchanger, such        that the phase separator is configured to receive a partially        cooled fluid from the heat exchanger, wherein the liquid outlet        of the phase separator is in fluid communication with a first        intermediate fluid inlet of the intermediate section of the heat        exchanger, wherein the gaseous outlet of the phase separator is        in fluid communication with a second intermediate fluid inlet of        the intermediate section of the heat exchanger, such that the        second intermediate fluid inlet of the intermediate section of        the heat exchanger is configured to receive at least a first        portion of gas coming from the phase separator, wherein the        transportable apparatus further comprises a third intermediate        fluid inlet of the intermediate section of the heat exchanger        that is configured to receive a second portion of gas coming        from the phase separator;    -   a third expansion valve is in fluid communication with, and        disposed inline between, the gaseous outlet of the phase        separator and a second intermediate fluid inlet of the        intermediate section of the heat exchanger;    -   a lower pressure natural gas outlet is in fluid communication        with the first natural gas outlet of the heat exchanger, wherein        the lower pressure natural gas outlet is configured to send a        stream warm natural gas received from the first natural gas        outlet to outside of the housing;    -   a liquid expansion valve is in fluid communication with, and        disposed inline between, the liquid outlet of the phase        separator and the first intermediate fluid inlet of the        intermediate section of the heat exchanger;    -   the heat exchanger is split into a first portion and a second        portion, wherein the warm end of the heat exchanger is disposed        in the first portion, wherein the cold end of the heat exchanger        is disposed in the second portion, wherein the intermediate        section is disposed in both the first portion and the second        portion;    -   the method may include an absence of compressing the natural gas        stream within the transportable apparatus;    -   the transportable apparatus comprises an absence of a rotating        compressor;    -   the transportable apparatus comprises an absence of rotating        machinery;    -   the transportable apparatus comprises an absence of electrically        powered compression or expansion devices;    -   the method may include an absence of a step of providing        external electric power to the transportable apparatus;    -   the step of providing the transportable apparatus comprises        loading the transportable apparatus on a truck or barge and        transporting the transportable apparatus from a first location        to a second location; and/or    -   the heat exchanger, the phase separator, the first refrigeration        supply, and the second refrigeration supply are all disposed        within the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, claims, and accompanying drawings. It is to be noted,however, that the drawings illustrate only several embodiments of theinvention and are therefore not to be considered limiting of theinvention's scope as it can admit to other equally effectiveembodiments.

FIG. 1 provides an embodiment of the present invention.

FIG. 2 provides an embodiment of the present invention, wherein thesecond refrigeration supply includes expanding a portion of theliquefied natural gas.

FIG. 3 provides an embodiment of the present invention, wherein thesecond refrigeration supply includes liquid nitrogen.

FIG. 4 provides another embodiment of the present invention having anexpansion turbine.

FIG. 5 provides an embodiment of the present invention having anexpansion turbine driving a gas booster.

DETAILED DESCRIPTION

While the invention will be described in connection with severalembodiments, it will be understood that it is not intended to limit theinvention to those embodiments. On the contrary, it is intended to coverall the alternatives, modifications and equivalence as may be includedwithin the spirit and scope of the invention defined by the appendedclaims.

There is a demand for low cost localized nano-scale (e.g., <10 mtd) LNGproduction. Typical current systems on the market for nano-scale LNGproduction utilize forms of closed loop cycles with a refrigerationcompressor that requires electrical consumption.

In one embodiment, the present invention proposes a solution forliquefaction of natural gas (LNG) which can be packaged (within size oftruck trailer, barge, etc. . . . ) and preferably requires “zero energy”consumption and contains no rotating machinery equipment. This saves onsetup of electrical equipment and operating maintenance.

In one embodiment, the apparatus can effectively achieve the goal ofliquefaction of LNG with no rotating machinery by utilizing the letdownenergy of available letdown stations. For example, one potentiallocation that could benefit from an embodiment of the present inventionwould include city gates where high pressure natural gas fromtransmission lines are letdown to low pressure distribution lines. Thisavailable letdown energy can be converted to refrigeration energy with acombination of pressure letdown valves described herein.

“Warm split”

Purified natural gas from a high pressure transmission pipeline(typically >20 bara) can be fed to a main exchanger (such as brazedaluminum), where it can be cooled to an intermediate temperature (e.g.,to between −40° C. to −70° C.) where heavy hydrocarbons (HHCs) areliquefied and separated in a separator. The HHCs can be re-warmed in theexchanger and sent to a medium pressure tail gas header or distributionpipeline (e.g., typically between 4 to 10 bara). Vapor from theseparator can be split into two streams. The first can be reduced inpressure through a control valve, re-warmed in the main exchanger andalso sent to the medium pressure natural gas header (distributionheader). In one embodiment, this expanded stream can provide a majoritysource of refrigeration for the system. The second vapor stream from theseparator can be further cooled and liquefied in the main exchanger toform the LNG product at the cold end.

In this embodiment, the separation of the vapor stream (first being sentto MP header and second being liquefied as product LNG) occurs at thesame temperature as the HHC separator. This removes headers anddistributors on the main exchanger thus simplifying its design comparedto having different temperatures for the vapor split and the HHCremoval. The impact is a small (<5%) loss in thermal efficiency, whichis justified by the small scale and simplified design.

In other embodiments, this HHC stream at the separator outlet can beprocessed as NGLs, or sent to the LNG production (depending on productconstraints of HHC freezing). In one embodiment, the re-warmed mediumpressure vapor from the separator can be used as a regenerating streamto remove impurities such as water and CO₂ from the adsorption unit. Inanother embodiment, the re-warmed low pressure vapor is mixed with thevaporized HHC stream.

“Cold Split(s)”

In one embodiment, the LNG leaving the cold end of the main exchangercan be split into three streams. The first stream can be reduced inpressure and sent to the LNG storage tank. The second can be reduced inpressure, vaporized and warmed against the natural gas being liquefiedin the main exchanger and sent to the MP header (e.g., 4-10 bara). Thethird can be reduced to a lower pressure (e.g., 1.1 to 2 bara) (toprovide the required final cold end cooling).

The combination of the two described “warm split” and “cold split”concepts yields a particular cooling curve to effectively produce LNGwithout a turbine.

In one embodiment, the Low Pressure natural gas return stream can besent to a pretreatment unit where it is burned as fuel to heat aregeneration stream. In one embodiment, the pretreatment unit removeswater and CO₂ from the natural gas feed for cryogenic processing.

In another embodiment, the final cold end cooling can be provided byvaporizing liquid nitrogen at the cold end of the main exchanger. LINcan be vaporized at approximately 6 bara and can be utilized as autility or instrument gas or vented to atmosphere. This is analternative to vaporizing a portion of the low pressure natural gas(e.g., 1.1 to 2 bara) if there is no demand for this fuel gas and if LINis available.

The product package shown in FIG. 1 describes both the low pressurenatural gas stream as well as the LIN injection at the cold end.However, embodiments of the invention may be practiced with only one ofthe refrigeration sources present. In certain embodiments, the inventioncan be designed as a standard product to accommodate a site with eitherresource, such that the apparatus will be enabled to work with either ofthe refrigeration sources (e.g., LIN or LP NG as fuel).

As shown in FIG. 3, the LIN demand can be on the order of 1 to 1.5 mtdcontinuous. The source of the liquid nitrogen may be trucked in by batchfrom external source, stored in a LIN tank inside the insulated cold boxpackage. As such, the typical external expensive double walled vacuumedinsulated storage tank is not required.

This cold box package, which can include the main exchanger, separator,valves and LIN tank, can be packaged into the size and shape of astandard shipping container.

In another embodiment, the first vapor stream from the HHC separatordescribed in the “warm split” above can be replaced by a natural gasstream letdown through a turbine. This turbine creates a cold vaporstream which can be warmed by heat exchange with the natural gas streambeing liquefied in the main exchanger. This significantly reduces theflow rate of natural gas required to be letdown. While this turbine addsa rotating machinery component, there is still no refrigerationcompressor needed, thereby requiring no electrical system and resultingin “zero energy” LNG production.

In one embodiment, this natural gas turbine can be connected to an oilbrake, or connected to a booster brake to recover additionalrefrigeration, or connected to a generator brake.

Referring to FIG. 1, a process flow diagram of an embodiment of thecurrent invention is shown. In FIG. 1, HP natural gas 4 can be withdrawnfrom high pressure natural gas pipeline 2 and sent to purification unit10 for purification of impurities such as water and CO₂ to form purifiednatural gas 12. In one embodiment, purification unit 10 can be locatedwithin housing 20. Purified natural gas 12 can then be introduced tohousing 20 via natural gas feed inlet 13, and then introduced to warmend of heat exchanger 30, where purified natural gas 12 is thenpartially cooled to a temperature effective for condensing heavyhydrocarbons. Partially cooled natural gas 32 is then removed from anintermediate portion of heat exchanger 30 and fed to phase separator 40under conditions effective for separating the natural gas from the heavyhydrocarbons. Top gas 42 is then withdrawn from the top of phaseseparator 40 and preferably split into two portions: first portion oftop gas 44 and second portion of top gas 46. First portion of top gas 44can be then introduced into cold split 30 b (see FIG. 2), and fullycooled and liquefied to form liquefied natural gas 50.

In one embodiment, liquefied natural gas 50 can then be split into twoor three streams: LNG product 64, first LNG stream 52 and optionallysecond LNG stream 54. LNG product 64 can be removed from housing 20 andthen expanded across LNG expansion valve 62 and stored in LNG storagetank 60.

One portion of the refrigeration for the apparatus can be provided byexpansion of first LNG stream 52 across first expansion valve 51. Afterexpansion, first LNG stream 52 is then warmed in heat exchanger 30 (orin the embodiment shown in other figures cold split 30 b and warm split30 a), wherein it is withdrawn from the warm end of heat exchanger 30 atfirst natural gas outlet 55, and then from housing 20 and optionallysplit into two streams, with first portion of warmed first natural gasstream 82 optionally being used to regenerate purification unit 10,while the remaining portion is expanded across warm expansion valve 84and combined with first portion of warmed first natural gas stream 82 toform medium pressure natural gas 86, before being introduced to mediumpressure natural gas pipeline 90.

In one embodiment, second refrigeration supply can be created byexpanding second LNG stream 54 across second expansion valve 53 andwarming second LNG stream 54 within heat exchanger 30, wherein it can bewithdrawn from heat exchanger 30 at second natural gas outlet 57 aswarmed natural gas 76.

In another embodiment, second refrigeration supply is accomplished withwarming of liquid nitrogen, and in certain embodiments, vaporizing theliquid nitrogen within heat exchanger 30. In this embodiment, LINdelivery truck 100 can input liquid nitrogen feed 68 to LIN storage tank70 by connecting to housing 20 via liquid nitrogen feed inlet 67. Whenrefrigeration is needed, the flow of nitrogen is started by opening LINcontrol valve 71 and flowing liquid nitrogen fluid 72 into cold split 30b via liquid nitrogen inlet 73. Liquid nitrogen fluid 72 can then bewithdrawn from warm split 30 a of heat exchanger 30 via nitrogen outlet59 as warmed nitrogen 74.

In one embodiment, second portion of top gas 46 can be expanded acrossthird expansion valve 47 to produce additional refrigeration (i.e.,third refrigeration supply). In one embodiment, third refrigerationsupply is configured to provide the predominant portion of coolingwithin warm split 30 a. As such, second portion of top gas 46 isintroduced into intermediate portion of heat exchanger 30, andpreferably combined with first LNG stream 52 within heat exchanger 30.While FIG. 1 shows second portion of top gas 46 combining with first LNGstream 52, those of ordinary skill in the art will recognize that thetwo streams could be within separate flow paths of heat exchanger 30.

In another embodiment, heavy hydrocarbons 48 can be withdrawn from thebottom of phase separator 40, expanded across liquid expansion valve 49to create additional refrigeration for warm split 30 a (i.e., fourthrefrigeration supply). As such, heavy hydrocarbons 48 can be introducedinto intermediate section of heat exchanger 30 and warmed within heatexchanger 30, wherein it can be combined with first LNG stream 52 andsecond portion of top gas 46 prior to exiting housing 20. In oneembodiment, heavy hydrocarbons 48, can be combined with first LNG stream52 and second portion of top gas 46 within heat exchanger 30. In apreferred embodiment, first portion of top gas 44, second portion of topgas 46, and heavy hydrocarbons 48 are all preferably expanded to thesubstantially same pressure.

In one embodiment, a portion of stream 46 following expansion in thirdexpansion valve 47 can be sent to storage tank 60 without being rewarmedin heat exchanger 30. In another embodiment, the portion of stream 46can be further cooled in heat exchanger prior to being sent to storagetank 60.

Referring to FIG. 2, a process flow diagram of an embodiment of thecurrent invention is shown, wherein the second refrigeration supply isaccomplished using expansion of LNG. In FIG. 2, 156 tpd of high pressurenatural gas is withdrawn at 40 bara from the high pressure natural gaspipeline. As shown in FIG. 1, it is cooled and then separated in phaseseparator. In this embodiment, 9 tpd of heavy hydrocarbons are expandedand warmed in warm split 30 a, while 139 tpd of second portion of topgas 46 are expanded and warmed in warm split 30 a. 8 tpd of firstportion of top gas 44 are then cooled in cold split 30 b with 5 tpd ofLNG being stored at 3 bara. In this embodiment, approximately 2 tpd offirst LNG stream 52 is expanded and warmed in cold split 30 b and warmsplit 30 a, and approximately 0.8 tpd of second LNG stream 54 isexpanded to 1.9 bara and then warmed in cold split 30 b and warm split30 a, wherein it can be used as fuel gas.

Referring to FIG. 3, a process flow diagram of an embodiment of thecurrent invention is shown, wherein the second refrigeration supply isaccomplished using expansion of LIN. In FIG. 3, in order to produce thesame amount of LNG (i.e., 5 tpd at 3 bara), only 140 tpd of highpressure gas is needed from the pipeline. In this embodiment,approximately 1.5 tpd of LIN, which can be stored at a temperature −176°C. can be expanded from 6.3 bara to approximately 6 bar, and warmed incold split 30 b and warm split 30 a before being introduced to anitrogen pipeline. In another embodiment not shown, it is possible toadjust the pressure of the nitrogen based on the need for nitrogenutility gas.

Referring to FIG. 4, a process flow diagram of an embodiment of thecurrent invention is shown, which includes a supplemental refrigerationsupply that includes natural gas expansion turbine 110. In FIG. 4,purified natural gas 12 can be split, outside or within heat exchanger30 into first portion of purified natural gas 15 and second portion ofpurified natural gas 16, with first portion of purified natural gas 15going to form LNG and first/second refrigeration supply. In thisembodiment, second portion of purified natural gas 16 is preferablypartially cooled in warm split 30 a and then expanded in natural gasexpansion turbine 110 to form expanded natural gas 112, which is thenfed into cold split 30 b and warmed therein. In another embodiment, aportion of expanded natural gas 112 can be direct either directly to LNGstorage tank 60 or cooled in heat exchanger 30 before being sent to LNGstorage tank 60.

While the embodiment shown in FIG. 4 does not include second portion oftop gas 46 and second expansion valve 53, those of ordinary skill in theart will recognize that second portion of top gas 46 and secondexpansion valve 53 could be included in this embodiment. While thisembodiment includes rotating equipment, the embodiment can still produceLNG without the need for any externally provided electricity for theprocess equipment. In the embodiment shown, natural gas expansionturbine 110 also can include oil brake B. While not shown, brake B maybe replaced by an electrical generator.

Referring to FIG. 5, a process flow diagram of an embodiment of thecurrent invention is shown, which includes a supplemental refrigerationsupply that includes natural gas expansion turbine 110 and natural gasbooster 120. In FIG. 5, purified natural gas 12 is again split intofirst portion of purified natural gas 15 and second portion of purifiednatural gas 16, but instead of second portion of purified natural gas 16being first expanded, in this embodiment, second portion of purifiednatural gas 16 can be compressed by natural gas booster 120, cooled inaftercooler, partially cooled in warm split 30 a and then expanded innatural gas expansion turbine 110 to form expanded natural gas 112,which is then fed into cold split 30 b and warmed therein. While theembodiment shown in FIG. 5 does not include second portion of top gas 46and second expansion valve 53, those of ordinary skill in the art willrecognize that second portion of top gas 46 and second expansion valve53 could be included in this embodiment. While this embodiment includesrotating equipment, including both a compressor and turbine, theembodiment can still produce LNG without the need for any externallyprovided electricity, since natural gas expansion turbine 110 powersnatural gas booster 120 via a common shaft.

The term “ambient temperature” if used herein refers to the temperatureof the air surrounding an object. Typically the outdoor ambienttemperature is generally between about 0 to 110° F. (−18 to 43° C.).

Efficiency data for the various embodiments described herein can befound in Table I below:

TABLE I Efficiency Data for Various Embodiments FIG. 2 FIG. 3 FIG. 4FIG. 5 (no turbine) (no turbine with LIN assist) 1 Turbine/oil brake 1Turbine/booster INLET NG FEED tpd 156.3 139.6 35.5 26.2 bara 40 40 40 40OUTLET LIN ASSIST tpd — 1.5 — — NG PRODUCT tpd 150.4 134.5 29.6 20.3(TAIL GAS) bara 6 6 6 6 NG PRODUCT tpd 0.8 0 0.8 0.8 (E.G., FUEL GAS)bara 1.9 — 1.9 1.9 LNG PRODUCT tpd 5 5 5 5 bara 3 3 3 3 ° C. sat sat satsat TURBINE BRAKE kW — — 38 32

The term “cryogenic gas” if used herein refers to a substance which isnormally a gas at ambient temperature that can be converted to a liquidby pressure and/or cooling. A cryogenic gas typically has a boilingpoint of equal to or less than about −130° F. (−90° C.) at atmosphericpressure.

The terms “liquefied natural gas” or “LNG” as used herein refers tonatural gas that is reduced to a liquefied state at or near atmosphericpressure.

The term “natural gas” as used herein refers to raw natural gas ortreated natural gas. Raw natural gas is primarily comprised of lighthydrocarbons such as methane, ethane, propane, butanes, pentanes,hexanes and impurities like benzene, but may also contain small amountsof non-hydrocarbon impurities, such as nitrogen, hydrogen sulfide,carbon dioxide, and traces of helium, carbonyl sulfide, variousmercaptans or water. Treated natural gas is primarily comprised ofmethane and ethane, but may also contain small percentages of heavierhydrocarbons, such as propane, butanes and pentanes, as well as smallpercentages of nitrogen and carbon dioxide.

While the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in light of the foregoing description. Accordingly, it is intendedto embrace all such alternatives, modifications, and variations as fallwithin the spirit and broad scope of the appended claims. The presentinvention may suitably comprise, consist or consist essentially of theelements disclosed and may be practiced in the absence of an element notdisclosed. Furthermore, if there is language referring to order, such asfirst and second, it should be understood in an exemplary sense and notin a limiting sense. For example, it can be recognized by those skilledin the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means thesubsequently identified claim elements are a nonexclusive listing (i.e.,anything else may be additionally included and remain within the scopeof “comprising”). “Comprising” as used herein may be replaced by themore limited transitional terms “consisting essentially of” and“consisting of” unless otherwise indicated herein.

“Providing” in a claim is defined to mean furnishing, supplying, makingavailable, or preparing something. The step may be performed by anyactor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

All references identified herein are each hereby incorporated byreference into this application in their entireties, as well as for thespecific information for which each is cited.

I claim:
 1. A method for the production of liquefied natural gas (“LNG”)using a transportable apparatus, the method comprising the steps of:providing a transportable apparatus, wherein the transportable apparatuscomprises a housing, a heat exchanger, a phase separator, a firstrefrigeration supply, and a second refrigeration supply, wherein thefirst refrigeration supply and the second refrigeration supply areconfigured to provide refrigeration within the heat exchanger;introducing a natural gas stream into the transportable apparatus at afirst pressure under conditions effective for producing an LNG stream;withdrawing the LNG stream from the transportable apparatus; andwithdrawing a warm natural gas stream from the transportable apparatus,wherein the warm natural gas stream is at a second pressure, wherein thesecond pressure is lower than the first pressure.
 2. The method asclaimed in claim 1, wherein the first refrigeration supply comprises afirst expansion valve, a first LNG inlet disposed on a cold end of theheat exchanger, and a first natural gas outlet disposed on a warm end ofthe heat exchanger, wherein the first refrigeration supply is in fluidcommunication with a liquid outlet disposed on the cold end of the heatexchanger, wherein the heat exchanger is configured to indirectlyexchange heat between a first LNG stream and the natural gas stream whenthe first LNG stream flows from the first LNG inlet to first natural gasoutlet.
 3. The method as claimed in claim 2, wherein the secondrefrigeration supply comprises a liquid nitrogen inlet disposed on thecold end of the heat exchanger and a nitrogen outlet disposed on thewarm end of the heat exchanger, and wherein the heat exchanger isconfigured to indirectly exchange heat between a liquid nitrogen fluidand the natural gas stream when the liquid nitrogen flows from theliquid nitrogen inlet to the nitrogen outlet.
 4. The method as claimedin claim 3, wherein the second refrigeration supply further comprises aliquid nitrogen storage tank in fluid communication with the liquidnitrogen inlet, such that the liquid storage tank is configured todeliver liquid nitrogen to the heat exchanger via the liquid nitrogeninlet.
 5. The method as claimed in claim 2, wherein the secondrefrigeration supply comprises a second expansion valve, a second LNGinlet disposed on the cold end of the heat exchanger, and a secondnatural gas outlet disposed on the warm end of the heat exchanger, andwherein the heat exchanger is configured to indirectly exchange heatbetween a second LNG stream and the natural gas stream when the secondLNG stream flows from the second LNG inlet to second natural gas outlet.6. The method as claimed in claim 5, wherein the first expansion valveis configured to expand the first LNG stream to a first LNG pressure,wherein the second expansion valve is configured to expand the secondLNG stream to a second LNG pressure, wherein the first LNG pressure ishigher than the second LNG pressure.
 7. The method as claimed in claim6, wherein the first LNG pressure is between 4 and 10 bara, wherein thesecond LNG pressure is between 1 to 2 bara.
 8. The method as claimed inclaim 1, wherein portable apparatus further comprises a natural gas feedinlet configured to accept a stream of pressurized natural gasoriginating from outside the housing, wherein the heat exchanger is influid communication with the natural gas feed inlet, such that the heatexchanger is configured to receive the stream of pressurized natural gasfrom the natural gas feed inlet, wherein the heat exchanger has a warmend, a cold end, and an intermediate section, wherein phase separatorhas a fluid inlet, a gaseous outlet, and a liquid outlet, wherein thefluid inlet is in fluid communication with a first intermediate fluidoutlet located in the intermediate section of the heat exchanger, suchthat the phase separator is configured to receive a partially cooledfluid from the heat exchanger, wherein the liquid outlet of the phaseseparator is in fluid communication with a first intermediate fluidinlet of the intermediate section of the heat exchanger, wherein thegaseous outlet of the phase separator is in fluid communication with asecond intermediate fluid inlet of the intermediate section of the heatexchanger, such that the second intermediate fluid inlet of theintermediate section of the heat exchanger is configured to receive atleast a first portion of gas coming from the phase separator, whereinthe transportable apparatus further comprises a third intermediate fluidinlet of the intermediate section of the heat exchanger that isconfigured to receive a second portion of gas coming from the phaseseparator.
 9. The method as claimed in claim 8, further comprising athird expansion valve in fluid communication with, and disposed inlinebetween, the gaseous outlet of the phase separator and a secondintermediate fluid inlet of the intermediate section of the heatexchanger.
 10. The method as claimed in claim 8, further comprising alower pressure natural gas outlet in fluid communication with the firstnatural gas outlet of the heat exchanger, wherein the lower pressurenatural gas outlet is configured to send a stream warm natural gasreceived from the first natural gas outlet to outside of the housing.11. The method as claimed in claim 8, further comprising a liquidexpansion valve in fluid communication with, and disposed inlinebetween, the liquid outlet of the phase separator and the firstintermediate fluid inlet of the intermediate section of the heatexchanger;
 12. The method as claimed in claim 8, wherein the heatexchanger is split into a first portion and a second portion, whereinthe warm end of the heat exchanger is disposed in the first portion,wherein the cold end of the heat exchanger is disposed in the secondportion, wherein the intermediate section is disposed in both the firstportion and the second portion.
 13. The method as claimed in claim 1,further comprising an absence of compressing the natural gas streamwithin the transportable apparatus.
 14. The method as claimed in claim1, wherein the transportable apparatus comprises an absence of arotating compressor.
 15. The method as claimed in claim 1, wherein thetransportable apparatus comprises an absence of rotating machinery. 16.The method as claimed in claim 1, wherein the transportable apparatuscomprises an absence of electrically powered compression or expansiondevices.
 17. The method as claimed in claim 1, further comprising anabsence of a step of providing external electric power to thetransportable apparatus.
 18. The method as claimed in claim 1, whereinthe step of providing the transportable apparatus comprises loading thetransportable apparatus on a truck or barge and transporting thetransportable apparatus from a first location to a second location. 19.The method as claimed in claim 1, wherein the heat exchanger, the phaseseparator, the first refrigeration supply, and the second refrigerationsupply are all disposed within the housing.
 20. The method as claimed inclaim 1, wherein the combined flow rates of refrigerant through thefirst refrigeration supply and the second refrigeration supply are lessthan 10% of the flow of the natural gas stream into the transportableapparatus at the first pressure.
 21. The method as claimed in claim 1,wherein the warm natural gas stream at the second pressure is burned asfuel in a purification unit.